Dielectric Constant Increases Research Articles

Photophysical investigation of a donor-acceptor based Schiff base in solvents of varying polarities

The present work reports detailed photophysics of excited state intramolecular charge transfer process in donor-acceptor system, namely, 7-((E)-((E)-3-(4 (dimethylamino)phenyl)allylidene) amino)-4-(trifluoromethyl)-2H-chromen-2-one (DPAATC) by steady state absorption, fluorescence and time resolved spectroscopy in combination with density functional theory calculations. Large fluorescence spectral shift observed in more polar solvents and large calculated excited state dipole moment clearly indicates an efficient charge transfer occurring from the donor group to the acceptor moiety in the excited state compared to the ground state. Effect on addition of acid and pH variation studies on steady state spectral properties further reveals charge transfer character. Fluorescence decay increases with increase in solvent dielectric constant in protic solvents which means the higher the polarity, the more is the stability of the probe. The HOMO and LUMO molecular orbital picture for the optimized ground state, donor twisted and acceptor twisted geometry are obtained at density functional theory level using B3LYP functional and 6-311+g(d,p) basis set which also support excited state intramolecular charge transfer process. The molecular electrostatic potential maps for the optimized ground state, donor twisted and acceptor twisted geometry shed insight on the electrostatic potential and charge distribution in a system which gives information about the reacting site of the probe and nature of the reaction.

Numerical simulation of thermal and dielectric properties for SiO<sub>2</sub>/polytetrafluoroethylene dielectric composite

Coefficient of thermal expansion (CTE) and dielectric constant for the SiO<sub>2</sub>/polytetrafluoroethylene (SiO<sub>2</sub>/PTFE) dielectric composite are mainly influenced by their filling content, and how to accurately predict the effect is still a great challenge untill now. In this work, the CTE and dielectric constant of SiO<sub>2</sub>/PTFE dielectric composite are systematically investigated by numerical simulation. The results show that with the increase of SiO<sub>2</sub> content, CTE of SiO<sub>2</sub>/PTFE dielectric composite decreases, and the dielectric constant increases, which are in good agreement with the data reported in the literature (Han K K, Zhou J, Li Q Z, Shen J, Qi Y Y, Yao X P, Chen W <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1007/s10854-020-03449-w">2020 <i>J. Mater. Sci. Mater. Electron.</i> <b>31</b> 9196</ext-link>). The 30% (volume fraction) solid SiO<sub>2</sub> sphere (SSS)/PTFE dielectric composite is the smallest CTE of 7.5×10<sup>–5</sup> K<sup>–1</sup>, while 10% (volume fraction) hollow solid sphere (HSS)/PTFE possesses the smallest dielectric constant of 2.06. The CTE of SiO<sub>2</sub>/PTFE dielectric composite may decrease when the SiO<sub>2</sub> distribution is dense at the bottom. The large aspect ratio of SiO<sub>2</sub> filler may reduce CTE<sub><i>x</i></sub> of SiO<sub>2</sub>/PTFE dielectric composite. The molding parameters have little effect on the thermal expansion coefficient of the solid SiO<sub>2</sub>/PTFE composite dielectric material. This work provides a clear insight into the controlling of CTE and dielectric constant of SiO<sub>2</sub>/PTFE dielectric composite by adjusting its microstructure.

Structural, optical and electrical properties of undoped and doped (Al, Al + Mn) ZnO nanoparticles synthesised by green combustion method using terminalia catappa seed extract

This paper presents the synthesis of undoped and doped (Al, Al + Mn) ZnO nanoparticles by green combustion method using Terminalia Catappa seed extract as a novel fuel and Zinc nitrate as a precursor, Aluminum nitrate and Magnesium chloride was used as dopant. Synthesized undoped and doped ZnO nanoparticles were characterized by XRD, FESEM, FTIR, UV-visible spectroscopy and impedance spectroscopy. The XRD study of undoped and doped (Al, Al + Mn) ZnO nanoparticles exhibits hexagonal wurtzite structure with high crystallinity. The crystallite size increases from 37.5 nm to 39 nm for Al doping and decreased to 30.5 nm for Al + Mn doped ZnO nanoparticles. Mean grain size of undoped ZnO nanoparticles was found to be 32.5 nm. For Al doped ZnO nanoparticles mean grain size increases (42.9 nm) and then decreases (21.25 nm) for Al + Mn doped ZnO nanoparticles. FTIR studies confirms the formation of Zn-O bond at 462, 455 and 439 cm−1 for both undoped and doped ZnO nanoparticles. The optical band gap was found to be 3.25, 3.2 and 2.54 eV for undoped and doped (Al , Al + Mn) ZnO nanoparticles respectively. The dielectric properties and conductivity studies were carried for undoped and doped (Al, Al + Mn) ZnO nanoparticles at various fixed temperatures (50 to 350 °C) by varying frequency from 10 Hz to 8 MHz. Dielectric constant increases with rise in temperature and, dielectric constant decreases with rise in frequency and remains constant at higher frequency. At lower frequencies AC conductivity was constant and increases as the frequency increases. Grain and grain boundary resistance for the synthesised ZnO nanoparticles were studied by complex impedance analysis and result exhibits a decrease in grain resistance with rise in temperature. The ZnO nanoparticles doped with Al shows improved microstructural properties, decreased optical band gap and activation energy. Hence these nanoparticles are suitable material for sensors and optoelectronics applications.

Electrical conduction of PMMA/PLA doped lithium bis(oxalato) borate based hybrid gel polymer electrolyte

The present work highlights the investigation of electrical conduction properties of gel polymer electrolyte (GPE) based poly(methyl) methacrylate (PMMA) and poly(lactic) acid (PLA) blend doped with various compositions of lithium bis(oxalato) borate. The impedance analysis revealed the GPE systems exhibit maximum ionic conductivity of 1.37 × 10−3 S cm−1 for sample PLi20. The electrical properties based on the dielectric permittivity of entire samples decreased with increasing frequency and followed the trend of ionic conductivity. Further analysis was carried out to determine the dielectric response at different temperatures, focusing on the most conducting sample (PLi20). Both dielectric constant and loss increase with the increasing temperature, which suggested that total polarization has occurred. In conclusion, the samples with 20 wt% composition of LiBOB exhibit the highest conducting properties which significantly provides good electrical performance for the application in energy storage devices.

Conduction Mechanism and Dielectric Properties in Polyaniline/Titanium Dioxide Composites

The conductivity and dielectric properties of polyaniline (PANI) and PANI/TiO2 composites have been studied over a temperature range (313-393 K) and frequency range (25 Hz- 50 MHz). The nature of temperature and frequency-dependent conductivity can be explained by Jonscher’s universal power law and used to find the related parameters such as frequency exponent (s), dc conductivity (σdc), and crossover frequency (ωH). Besides, the frequency exponent analysis through a distinct model suggests that the conduction occurred through small polaron tunnelling in all compositions and at different temperatures. On the other hand, the enthalpy of migration (Hm), dissociation enthalpy of cation from its indigenous location alongside a compensating center (Hf), and the activation energy were also calculated using the Arrhenius relation. The temperature-dependent dc conductivity was examined in the framework of the theoretical model; Mott’s variable range hopping model (VRH) and experimental results were in good agreement with the 3-dimensional VRH model. As a function of temperature, dielectric constants (ε’ and ε”) increase while decreasing with an increasing dopant. Being such a high dielectric constant value, these composites can be used as frequency converters, modulators, and dielectric amplifiers.

Enhanced dielectric and optical properties in Al-substituted KBiFe2O5

We report a significant effect of Aluminum (Al3+) substitution on the structural, optical and dielectric properties in brownmillerite KBiFe2O5 (KBFO) multiferroic. Polycrystalline samples of KBiFe2-xAlxO5 (x = 0, 0.2) are synthesized by citrate combustion method. From the Rietveld refinement of X-ray diffraction analysis, both the samples are found to crystalize in a monoclinic structure possessing P2/c space group. The calculated crystallite size from the Scherer’s formula is found to decrease with Al doping. The surface morphology reveals that, multiple grains of different sizes are present in all the samples and the average grain size is reduced with substitution. The optical band gap decreases from 1.739 eV to 1.715 eV with x = 0.2 of Aluminum. Furthermore, the temperature dependent Dielectric constant (ε) and dielectric loss (tan δ) of KBiFe2-xAlxO5 are investigated in a temperature range (300–773 K) at 100 Hz and 1 KHz frequency shows a substantial variation followed by a transition at around 550 K for all the samples. A comparative analysis for both the systems reveals that, for x = 0.2 of Al, an order of increase of dielectric constant appears as compared to the parent system. Additionally, the dielectric loss is also found to decrease with doping as compared to pure KBFO.

Performance investigation of hetero gate dielectric DGTFET with drain pocket for analog/RF applications

This work examined a double gate Tunnel FET (DGTFET) employing a heterogeneous gate dielectric (HD) scheme and a drain pocket (DP) for analog/ RF applications. Two different gate dielectric HfO2 (εox = 21) and Al2O3 (εox = 10) are compared with DP-DGTFET (without HD) for ION, IAMB, Vth, SS, and ION/IOFF. It is observed that as the value of the dielectric constant increases, ION rises with the reduction in the width of the tunneling barrier at the source-channel interface. However, ION/IOFF ratio for Al2O3 based device is two orders of magnitude better than the device employing HfO2. Further RF performance figures of merits (FOMs) CG, UPG,fT, Fmax, Gma, and admittance parameters are also inspected for all devices under concern using TCAD simulations.

STUDY OF AC/DC CONDUCTIVITY OF POLY VINYL CHLORIDE PVC AND EC, EC/PVC CONDUCTION MECHANISMS RESPONSIBLE FOR THE CONDUCTIVITY

The current work investigates the AC and DC conductivity constant of PVC and EC samples (3:1) at many constant temperatures in the frequency range (323K to 363K). The ndings were presented in graph form. The dielectric constant increases with temperature increase at constant frequencies, Dielectric constant decreases with frequency increases, and AC conductivity increases with frequencies at different constant temperatures. The frequencies reach almost saturation values as the ultimate 1MHz value reaches. The AC conductivity increases with the increase in frequency has been observed.

Theoretical Study of Solvent Effects on the Electronic and Thermodynamic Properties of Tetrathiafulvalene (TTF) Molecule Based on DFT

Tetrathiafulvalene () is an organosulfur compound used in the production of molecular devices such as switches, sensors, nonlinear optical devices and rectifiers. In this work, a theoretical study on the effects of solvent on TTF molecule was investigated and reported based on Density Functional Theory (DFT) as implemented in Gaussian 03 package using B3LYP/6-31++G(d,p) basis set. Different solvents were introduced as a bridge to investigate their effects on the electronic structure. The HUMO, LUMO, energy gap, global chemical index, thermodynamic properties, NLO and DOS analysis of the TTF molecule in order to determine the reactivity and stability of the molecule were obtained. The results obtained showed that the solvents have effects on the electronic and non-linear-optical properties of the molecule. The optimized bond length revealed that the molecule has strong bond in gas phase with smallest bond length of about 1.0834Å than in the rest of the solvents. It was observed that the molecule is more stable in acetonitrile with HOMO-LUMO gap and chemical hardness of 3.6373eV and 1.8187eV respectively. This indicates that the energy gap and chemical hardness of TTF molecule increases with the increase in polarity and dielectric constant of the solvents. The computed results agreed with the results in the literature. The thermodynamics and NLO properties calculation also indicated that TTF molecule has highest value of specific heat capacity (Cv), total dipole moment () and first order hyperpolarizability () in acetonitrile, while acetone has the highest value of entropy and toluene has a slightly higher value of zero point vibrational energy (ZPVE) than the rest of the solvents. The results show that careful selection of the solvents and basis sets can tune the frontier molecular orbital energy gap of the molecule and can be used for molecular device applications.

Swift Heavy ion irradiation effects on dielectric constant and dielectric loss in poly (ether ether ketone) (PEEK)

The dielectric constant (ε') and dielectric loss (ε״) of pristine and C5+ (70 MeV) ion irradiated samples of the PEEK have been investigated with the variation of temperature at different frequencies (100 Hz, 1 kHz, 10 kHz and 100 kHz). The maxima are obtained around 170 oC in dielectric constant (ε') vs. temperature (T) curve. This relaxation is linked with the movement of ketone (>C=0) dipoles linked to the main chain. The irradiation of polymers increases the orientational polarization due to increase in number of dipoles with fluence. The increase in dielectric constant (ε') and dielectric loss (ε'') is attributed to chain scissioning at higher fluence which results in an increase of free radicals and unsaturations. Copyright © 2018 VBRI Press.

Optical properties of InAs, InSb and InAs[formula omitted]Sb[formula omitted] (x=0.25, 0.5, 0.75) alloys under strain

Applying hydrostatic and biaxial lattice expansion, the optical properties of InAs, InSb and their ternary alloys InAsxSb1−x have been investigated using density functional theory by employing the WIEN2k package. Under hydrostatic lattice expansion, we observe a conversion to narrow or zero band gap semiconductors, while under biaxial lattice expansion a conversion to topological semiconductors occurs. We further investigate how the optical properties, investigated within the random phase approximation, changes upon the transformation to topological semiconductors, narrow or zero gap semiconductors. Under hydrostatic lattice expansion, for all compounds except for InAs, the static dielectric constant increases linearly. According to our results, moderate biaxial lattice expansions between 1% to 4% cause a conversion to topological semiconducting state while the static dielectric constant of these compounds is found to increase smoothly during the transformation. With the strain increasing, the optical absorption spectra can be red-shifted significantly , and the optical absorption can be enhanced in some regions of electromagnetism spectrum.

Origin of the thickness-dependent electric properties of BiScO3-PbTiO3 piezoceramics near the morphotropic phase boundary

The mechanism of thickness dependence electric properties for BiScO3-PbTiO3 ceramics with morphotropic phase boundary has been investigated. With increasing the sample thickness from 0.2 mm to 1.0 mm, the dielectric constant and piezoelectric coefficient increase by 39% and 36%, respectively, and then become stable with further increase of the sample thickness up to 2.0 mm. Both XRD patterns and Raman spectra show the lattice distortion of tetragonal phase decreases with the thickness. Quantitative analysis of XRD patterns of ceramics with different thicknesses reveal that enhanced electric properties with sample thickness are owing to the improved contributions from lattice distortion, irreversible domain switching and irreversible phase transition from tetragonal to rhombohedral phase with the increases of thickness, which is quite different from the decreased domain size in PMN-PT single crystal. These results not only provide a new mechanism, but also give an important basis for piezoelectric transducer design based on BiScO3-PbTiO3 ceramics.

High ionic conductivity and UV blocking in nanosized Li3 (1−x)Na3x VO4 superionic conductors

The effect of alkali metal doping on the electrical conductivity of Li3(1−x)Na3x VO4 (x = 0.0, 0.2, 0.4 and 0.6) is the axiom of this paper. The samples are synthesized using the conventional solid-state reaction technique. The X-ray diffraction results show the polycrystalline behavior of alkali-doped lithium vanadate (Li3VO4). It was also observed that sodium (Na+) ions have not shown their presence in the diffraction pattern, which indicates that alkali metal ions were well substituted in the interstitials and did not disturb the crystal planes of the lithium vanadate matrix. The X-ray diffraction studies also suggest an increment in the crystallite size of the prepared samples. The optical study shows excellent absorbance in UV range (200–300 nm) and also that with an increase in the alkali-doping concentration, shifts absorbance peaks slightly toward higher wavelengths, suggesting enhancement in the particle size. In these alkali-doped samples, it was observed that ionic conductivity decreases, and conversely, the dielectric constant and loss tangent increase subsequently with an increase in the sodium doping concentration due to the ionic radius of the dopant metal. High ionic conductivity within the range 1.1374 × 102–7.9326 × 100 Ω−1 m−1 (99.98% of total conductivity) is obtained in superionic phase of the material. These materials can be utilized in field of capacitors, transparent battery and electrode for batteries.

Exploring the characteristics of SnO2 nanoparticles doped organic blend for low cost nanoelectronics applications

The PVA/PVP/SnO2 nanostructure films were fabricated using the casting technique. The structure, dielectric and optical characteristics of PVA/PVP/SnO2 nanostructures were studied for pressure sensors. Results of studying the dielectric characteristics showed that the dielectric constant, dielectric losses and electrical conductivity of blend are enhanced with the rise of SnO2 nanoparticles (NPs) content. The dielectric constant and dielectric losses are reduced, while the conductivity is risen with the increase in frequency. The dielectric constant increases from 2.53 to 7.41, and dielectric losses rise from 0.5 to 2, while the conductivity increases from 2.82·10–11 S/cm up to 1.11·10–10 S/cm. The results of measuring the optical characteristics have indicated that the absorbance rises with increasing the SnO2 NPs content. The energy gap of blend has been reduced from 4.9 down to 4.65 eV with the rise in SnO2 NPs content. The optical constants have been improved with the rise in SnO2 NPs content. Results of studying the pressure sensors have shown that their capacitance grows with the pressure increase.

The Unusual Dielectric Response of Large Area Molecular Tunnel Junctions Probed with Impedance Spectroscopy

AbstractThe dielectric behavior of organic materials at molecular dimensions can be vastly different than their bulk counterparts and therefore it is important to investigate and control the dielectric response of molecular‐scale materials for a large variety of applications. Large‐area molecular junctions are explored to study the charge transport mechanisms with unprecedented detail and to demonstrate novel functionalities. Therefore, large‐area molecular junctions are, in principle, a promising platform to study the dielectric effects at the molecular scale. This review summarizes recent progress on the measurements and understanding of the dielectric behavior of molecular systems and how they behave differently from their bulk properties. This review introduces, briefly, the concepts of impedance spectroscopy (IS) and how this technique can be applied to study the dielectric response of solid‐state large‐area molecular junctions. This analysis gives new insights in the factors that determine the dielectric constant of monolayers (including collective electrostatic effects and how the dielectric constant increases with monolayer thickness), how IS gives new insights into the role of defects, and the factors that contribute to the molecule–electrode contact resistance. This review ends with an outlook highlighting interesting future directions.

Impact of dielectric properties on ionic conductivity of Ce0.9Sm0.1O1.95 via defect interaction

This study mainly investigates the defect interaction mediated ionic conductivity of Ce0.9Sm0.1O1.95. The ionic conductivity mainly depends on the concentration of free oxygen vacancies. The formed oxygen vacancies are bounded with dopant cations due to columbic interaction which depends on the dielectric constant of the material. With the rise in temperature dielectric constant increases and dopant–vacancy association decreases. Consequently, ionic conductivity increases with temperature due to the enhancement of concentration of free oxygen vacancies. The association and migration energy decrease at higher temperature.

KINETICS AND MECHANISM OF THE OXIDATION OF L-ASCORBIC ACID BY POTASSIUM TRISOXALATOFERRATE (III) TRIHYDRATE IN AQUEOUS HYDROCHLORIC ACID MEDIUM

The kinetics of the oxidation of K3[Fe(C2O4)3].3H2O by L-ascorbic acid has been studied in aqueous acidic medium. The stoichiometric studies showed that 1 mole of H2A was oxidized for every 2 moles of Fe(C2O4)33- reduced. Under pseudo-first order conditions of H2A >> Fe(C2O4)33-, the reaction was found to have first order dependence on each of the reactants, giving second order overall. The reaction rate was found to be directly dependent on acid concentration and increased with increase in ionic strength of reaction system. It was also evident that increase in dielectric constant of the reaction medium (D) enhanced the reaction rate and addition of CH3COO-, HCOO-, Mg2+and Li+ catalyzed the rate of the reaction. The oxidation of L-ascorbic acid by potassium trisoxalatoferrate (III) trihydrate is rationalized in terms of absence of ion pair complex formation with outer-sphere reaction pathway characteristics.

Ultra low loss (Mg1 − xCax)2SiO4dielectric ceramics (x = 0 to 0.15) for millimeter wave applications

Abstract(Mg1 − xCax)2SiO4dense ceramics (x ≥ 0.15) were prepared, and their microwave dielectric characteristics were investigated together with the structure evolution. The sintering temperature for Mg2SiO4ceramics was reduced significantly with Ca2+substitution. (Mg1 − xCax)2SiO4ceramics exhibited a small increase in dielectric constant (εr) correlated with increased crystallite size, and ultra‐high quality factorQfvalue was achieved throughout the compositional range. Temperature coefficient of resonant frequency (τf) was considerably tuned from −70 ppm/°C to −33 ppm/°C, and this improvement was deeply linked with the decreased bond valance. At x = 0.075, (Mg1 − xCax)2SiO4ceramics exhibited the best combination of microwave dielectric characteristics:εr = 7.2,Qf = 199,800 GHz at 26 GHz,τf = −33 ppm/°C. The present ceramics could be expected as promising candidate of dielectric materials for millimeter wave applications.

Theoretical insights of solvent effect on tautomerism, stability, and electronic properties of 6‐ketomethylphenanthridine

AbstractIn this manuscript, the influence of solvent on stability and electronic properties of enolimine, enaminone, and iminone forms of 6‐ketomethylphenanthridine is theoretically investigated using polarizable continuum model (PCM). Here, PCM is used during optimization of structures of tautomeric forms in solution. Water, ethanol, acetone, acetonitrile, chloroform, diethyl ether, dichloromethane, and dimethyl sulfoxide are chosen as solvent. The calculations are performed at M06‐2X/6‐311++G(d,p) level. In gas phase and in the solvents, the stability of tautomers increases as enaminone > enolimine > iminone. The topological properties of electron charge density are also studied for better understanding of stability of tautomers. It is observed that the stability of tautomers is diminished by increasing dielectric constant of solvent. Also, the increase in dielectric constant of solvent kinetically and thermodynamically facilitates the enolimine ⇌ enaminone tautomerization. To obtain more valuable information on stabilities of tautomers in water phase, the PCM calculations have also been performed with one water molecule. At M06‐2X/6‐311++G(d,p) level of theory, the stability of complexes is amplified as enaminone–water > iminone–water (V) > iminone–water (IV) > enolimine–water. The relationships between dielectric constant of solvent and some electronic properties of tautomers such as band gap, electron affinity, electrophilicity index, first ionization energy, electronic chemical potential, chemical softness, and hardness are also investigated.

Inverse Proportionality of Thermal Conductivity and Complex Permittivity to Filler-Diameter in Epoxy Resin Composites with Silica

We prepared six kinds of epoxy resin nanocomposites with silica and an epoxy resin with no silica. The nanocomposites contain silica with different diameters (10, 50, and 100 nm) while their silica contents are 1, 5, 10, and 20 vol%. At 25 and 100 °C, the thermal conductivity has a nearly proportional dependence on the silica content and exhibits an almost reciprocal proportionality to the diameter of the silica. The latter result indicates that the interaction at filler-resin interfaces plays a significant role in heat transfer. However, this view contradicts an easy-to-understand thought that the filler-resin interfaces should work as a barrier for heat transfer. This in turn indicates that the interaction at filler-resin interfaces controls the bulk properties of the resin when the filler is in a nm size. Although the dielectric constant increases with the addition of the silica filler, its increment from the resin with no silica is the smallest in the resin with the 10-nm silica. Therefore, the addition of the 10-nm silica is adequate for electrical insulation purposes.